In the dental impression is a process in which the rows of teeth are readjusted in detail separately by means of an impression material. Depending on the intended use of the impression, there are different impression materials. These are applied to a carrier, impression tray, applied and then slipped over the row of teeth. Curing takes up to 5 minutes. Then the dental impression can be taken out of the mouth. Subsequently, the impression is sent to a dental laboratory and used there for further use.
The dentist needs a dental impression for various reasons, for example
to document the situation before prosthetic work and before beginning orthodontic treatment
for the planning of dentures
for the diagnosis of dental and jaw malpositions (KFO)
after completion of a longer therapy
for the production of dentures and orthodontic appliances
for the production of temporaries
Depending on the required accuracy, different methods and materials are used for taking impressions.
Whereas a fast alginate impression is sufficient for the documentation, treatment planning and presentation of the opposing jaw in dentures, a multi-step procedure is required for the impression of the situation after preparation for the acquisition of a crown or bridge.
In the case of the classic alginate impression, a suitable impression tray is selected first, which can then be adapted to the patient situation by means of silicone walls, if necessary. A bonding agent (alginate adhesive) is applied to the spoon while the impression material is mixed and then placed in the spoon. The alginate-filled spoon is pressed into the row of teeth until the impression has hardened and is then carefully removed. After disinfecting the impression, a plaster model can be produced.
Precision impressions are a bit more elaborate. To ensure that the crown margin or implant prosthetics fits exactly in the patient's mouth, absolute dryness and a more accurate impression material is used as alginate.
For draining, the gums around the tooth or implant are first anesthetized, then a gum-holding thread is inserted which should be at least 10 minutes.
Previously, a matching impression tray was selected or the laboratory made an individual tray made of plastic. After the application of the primer, the spoon is filled with eg Impregum ™ or Aquasil ™ in half and a syringe.
Before the spoon is pressed into the row of teeth, the dentist with the filled syringe surrounds the marginal areas, which must be precisely represented. The curing of these prints takes much longer than an alginate impression and they become very hard, making removal more uncomfortable and difficult.
Another special feature is the impression of the edentulous jaw for the production of a complete denture (in the following the technique taught at the University of Frankfurt am Main is described):
After a situation impression with alginate for the production of models, which serve the production of individual spoons, the actual impression of the edentulous jaws is made. First, the edge is completely molded, then the entire jaw is imprinted.
In contrast to the abovementioned impression forms, in which the patient should not stir, in this impression movement of the jaw and facial muscle nature is desired. As long as the impression hardens, the dentist prompts the patient to perform various movements, such as sticking out his tongue, smirking, lips, saying Ah, swallowing. This is repeated until the soft tissue is completely imaged, as this is the only way to create a well-fitting prosthesis.
The setting time of the impression materials depends on the manufacturer's instructions.
Alginate is usually cured after about 2 minutes, while Impregum ™ and Aquasil ™ take about 7 minutes.
Luralite ™, which is used for total denture impressions, cures after 6 minutes.
However, due to the different steps for alginate, you should plan for about 5-10 minutes and for precision impressions at least 30 minutes. Depending on the situation and "cooperation" of the patient, impressions may take much longer.
The most common is the alginate impression to illustrate the situation. Alginate is a powder of algae and silica components that binds with water and is made in different colors. Typical is the minty taste and the quite elastic consistency.
High-viscosity precision impression materials include Impregum ™ (purple polyether) or Aquasil ™ (green and yellow A-silicone), which set without water and are very hard.
For full-denture functional impressioning, for example, GC ™ Iso functional sticks are used for the rim and Luralite ™ for the base. Both are pink, while the former is wax-like deformable by heating and the latter sets on Eugenolbasis.
For teeth that are already relaxed, a precision impression with Impregum ™ or Aquasil ™ can further loosen up to tooth loss. Therefore, either digitally molded or resorted to a softer material.
For situation impressions with loose teeth alginate is suitable. If increased accuracy is required, special impression materials can be used, such as Impregum Soft ™ or Express Penta ™ Putty, which are easier to demold.
A digital dental impression is created by a special camera that scans the teeth (hence also called "intraoral scan").
This technique is the most modern, but it can not be applied in all situations. For implant work and crowns or bridges whose boundaries are not below the gingival margin. but they are quite good.
Depending on the manufacturer, the pine to be molded must be dusted with powder after drying or not. Then the dentist leads the camera over the row of teeth. The scanning success can be tracked on the PC screen. If necessary, both scanned jaws can be put together on the PC. The 3D models calculated on the PC can be converted into plastic by a 3D printer. Then the dentures can be manufactured conventionally in the laboratory.
Some systems allow the direct production of dentures after planning on the PC by coupling with a milling machine that produces ceramic crowns, ceramic inlays or plastic rails directly in the field (Ex: CEREC).
The digital impression is not taken over by the statutory health insurance companies.
Depending on whether both jaw or only single teeth are scanned and which system is used in practice, the cost can be between 20 and over 50 euros.
The gagging is caused by the impression material, which is pressed to the palate. Since the digital dental impression is used without impression materials, the gagging usually remains.
If no intra-oral scan is possible, there are several possibilities. to suppress the gagging:
Shaping in an upright position (when looking down slightly)
conscious breathing through the nose
Distraction: wiggle your toes, count down in the head of 1000, and so on.
by correct dosage and filling of the spoon, the gagging can be reduced